1. Field of the Invention
The present invention relates to an optical head, capable of being integrated, of the optical coupler type working in transmission and reception at one and the same light wavelength that is conveyed by an optical fiber. This optical coupler, which is designed so that it can be directly integrated into the subtrate of a hybrid circuit, is noteworthy for the high degree of isolation between its two channels.
In the basic scheme of a system for the exchange of data by optical fiber, a single optical fiber connects two laser diode/photodiode sets, each located at one end of the optic fiber: in a first direction of exchange, the information elements sent out in the form of light pulses by a laser at first end are detected by a photodiode at a second end, and conversely in a second direction of exchange. The lasers can also be replaced by light-emitting diodes or LEDs.
When there is only one optical fiber for two communications channels, two systems have to be placed at the ends of the fiber: these systems are called couplers because they couple the laser and the photodiode to the fiber.
2. Description of the Prior Art
There are many known types of couplers, based on different principles, but it has appeared to be worthwhile that they can be integrated into the substrate of a hybrid circuit. The U.S. Pat. No. 5,123,067 by the present Applicant, describes an optical head with two dimensions (taken in the plane of a receiver hybrid circuit) in which the thickness of the semiconductor chips, lenses and optical fiber is considered to be negligible, this thickness being, in any case, of the same order of magnitude as the thickness of the components fixed to the hybrid circuit.
One drawback of optical couplers is related to the very great difference between the level of light energy sent out by the laser and the level of energy received by the photodiode. As a rule, in telecommunications, the distance between two couplers ranges from 1 to 25 kilometers, which considerably attenuates the light energy emitted by a laser, because it is absorbed in the core of the optical fiber. Even if the data exchange system is used with a small length of optical fiber, it is nevertheless a fact that, by virtue of the reversibility of the optical paths, a light ray sent out by the laser of a coupler can get partially reflected, on one of the many couplers of the diopter and to return to the detection photodiode of this same coupler. There is therefore poor isolation between the channels, giving rise to the equivalent of telephonic cross-talk, and a coupler detects a part of the signals that it sends out in parasite form.
The object of the invention is therefore an optoelectronic device, of the optical head or optical coupler type, comprising a light transmitter component and a light receiver component, this device having a structure and an organization such that the parasitic light rays which get reflected on the different diopters existing in the device do not travel on the same optical path as the incident rays, thus leading to a high degree of isolation between the transmission and reception channels. According to this structure, the detector component is no longer subjected to parasitic dazzling from the transmitter component that it neighbors in the same coupler.